Coherency limits of different transceivers within USRP X310 as a radar node

Diverse literature agrees on the advantages that multiple antennas and, thereby, multi-channel diversity brings into a modern radar system. Modern multichannel USRPs are suitable platforms for realisation of diverse radar demonstrators. However, coherency plays an essential role for accurate radar detection and tracking. This paper focuses on determining the stability of multi-channel TwinRX and UBX receiver’s daughterboards within a single and two USRP devices. A common signal generator provides the same signal to all daughterboards and the relative coherency is measured between the received digitised signals. For each daughterboard the modified Allan deviation (MDEV), phase noise and fractional frequency are measured. The measurements show that all selected daughterboards are appropriate for radar applications having MDEV less than 80 fs, phase noise better than -98 dBc/Hz at 1 Hz frequency offset and fractional frequency is in the range of 10^-13.